Method of manufacturing aluminum coated ferrous base articles

ABSTRACT

A process for coating a ferrous metal article with aluminum including cleaning the ferrous article, applying to the surface of the ferrous article a flux of about 0.125 to 4% aqueous solution of an organic aromatic carboxylic acid having one carboxyl group and a phenolic hydroxyl group, drying the ferrous article and subsequently applying molten aluminum to the ferrous article. The coating process wherein the acid is salicylic acid or 5-chlorosalicylic acid employed in concentrations of about 1 to 4%. Applying the flux to the ferrous metal article surface by immersion of the article in a flux bath having a temperature of about 100 to 212* F. for a period of about 1 to 2 minutes.

United States Patent METHOD OF MANUFACTURING ALUMINUM COATED F ERROUSBASE ARTICLES 6 Claims, No Drawings U.S.Cl 117/51, 1 17/1 14 C, 148/23Int. Cl C23c 1/08, C23f 17/00 Field of Search ..1 17/51, 114

Primary Examiner-Alfred L. Leavitt Assistant Examiner-J. R. Batten, Jr.Attorney-Arnold B. Silverman ABSTRACT: A process for coating a ferrousmetal article with aluminum including cleaning the ferrous article,applying to the surface of the ferrous article a flux of about 0. l 25to 4% aqueous solution of an organic aromatic carboxylic acid having onecarboxyl group and a phenolic hydroxyl group, drying the ferrous articleand subsequently applying molten aluminum to the ferrous article. Thecoating process wherein the acid is salicylic acid or S-chlorosalicylicacid employed in concentrations of about 1 to 4%. Applying the flux tothe ferrous metal article surface by immersion of the article in a fluxbath having a temperature of about 100 to 212 F. for a period of about 1to 2 minutes.

1 METHOD OF MANUFACTURING ALUMINUM COATED FERROUS BASE ARTICLESBACKGROUND OF THE INVENTION 1. Field of the Invention This inventionrelates generally to a process for coating a ferrous metal article withaluminum and more specifically relates to the use of an aqueous solutionof an organic aromatic carboxylic acid as a flux bath.

2. Description of the Prior Art It has been known that desirableproperties may be provided to a ferrous article by coating the same withaluminum. Such coated articles not only provide improved resistance tooxidation and acid attack, but also reduce the likelihood of other formsof corrosion. In addition, such coatings provide increased electricalconductivity, reflectivity and an attractive surface appearance.

There are numerous known systems for applying an aluminum coating toaferrous article. Among the known systems are hot dipping,electroplating, spraying, cladding and casting of aluminum around thesteel article.

In general known systems provide for a preliminary cleaning of theferrous article. This is generally followed by fluxing and applicationof the molten aluminum, with appropriate intermediate rinsing and dryingsteps. See U.S. Pat. No. 2,738,289.

The cleaning stages may consist of an initial grit blasting to removescale and rust. It has been conventional to subsequently remove greaseand oils from the surface of the ferrous articles by an organic solvent,an alkaline cleaner or a vapor degrease. Subsequent to degreasing, ithasbeen known to treat the ferrous surface by acid pickling to removeoxidation products. This is generally accomplished by means of a strongacid, such as hydrochloric or sulfuric acids.

After the pickling operation, the ferrous surface is then conventionallyrinsed and dried. An appropriate flux is then applied to the cleanedferrous article surface in order to promote good bonding between thealuminum and the ferrous metal. Effective fluxing is essential toobtaining a uniformly bonded smooth aluminum coating on the ferrousarticle. Various materials have been employed in known'fluxes. The useof molten salt baths are disclosed in U.S. Pat. Nos. 2,544,671 and2,569,097. Various acid and alkaline materials have also been employedas fluxing materials. 1

One problem frequently resulting from use of an ineffective fluxmaterial is that the aluminum coating is not'effectively and uniformlybonded to the ferrous article. Also, improper fluxing has been known tocontribute to the production of a rough aluminum coating surfaceappearance which is aesthetically undesirable. Also, inadequate fluxcoverage on the ferrous article may result in regions of discolorationwhich will produce areas of brown staining on the aluminized ferrousarticle which will render the article unacceptable for most purposes.These problems become particularly acute with respect to articles havingan irregular configuration as uniformity is more difficult to attainwith respect to such articles.

It has been known that some fluxes suitable for use with some ferrousmaterials, such as mild steel, cannot be effectively employed with otherferrous materials, such as cast iron. The use of such limited purposematerials makes it more difficult for one to establish flexibility in asystem which is to be employed to coat various types of ferrousarticles.

SUMMARY OF THE INVENTION The process of this invention employs a uniqueflux composition which is adapted to provideuniform, effectiveprotection against oxidation, uniformly strong bonding of the aluminumcoating to the ferrous article and a smooth aesthetically pleasingcoating surface. After conventional surface cleaning of the ferrousarticle, the ferrous article is immersed in a flux bath of about 0.125to 4 percent aqueous solution of an organic aromatic carboxylic acidhaving one carboxyl group and a phenolic hydroxyl group. The article issubsequently dried and the molten aluminum is applied.

In the preferred forms the acid employed is salicylic acid or5-chlorosalicylic acid. The preferred acid concentrations are about 1 to4 percent. The flux bath is provided at a temperature of about 100 to212 F. and preferably about 160 to 212 F. The ferrous article isimmersed in the bath for a period of l to 2 minutes.

After the article is removed from the flux bath, it is dried andsubsequently molten aluminum is applied to the surface of the ferrousarticle as by immersion of the article in a molten aluminum bathmaintained at a temperature of about l,250 to 1,400 F. for a period of lto 2 minutes.

It is an object of this invention to provide a flux solution for use incoating a ferrous article with a uniformly bonded alu-v DESCRIPTION OFTHE PREFERRED EMBODIMENT The process of this invention contemplates thecoating of a broad range of ferrous materials, including mild steel andcast iron, with aluminum. Byway of preliminary treatment, th e ferrousarticle will preferably be cleaned in a conventional manner. Dependingupon the condition of the material and type of material, it may bedesirable to first grit blast the article to remove scale and rust. Thismay be followed by a conventional degreasing step employing conventionalmeans such as solvent degreasing, vapor degreasing or an alkalinecleaner. After the vapor degreasing, the specimen may be pickled in asuitable acid such as hydrochloric or sulfuric acid. The picklingoperation may be accelerated by employing a pickling solution at anelevated temperature. I

After the cleaning operations, the article is then rinsed with water,which is preferably hot'water, to remove all of the undesired residualmaterials and provide a uniformly cleaned oxide-free ferrous surface. Asthe clean ferrous article will, unless protected, deteriorate throughoxidation and other corrosion it is important that the article bepromptlyprotected with the flux treatment. The flux employed in thisinvention comprises an aqueous solution of about 0.125 to 4 percent ofan organic aromatic carboxylic acid having one carboxyl group and aphenolic hydroxyl group. This flux may be most conveniently applied byimmersion of the ferrous article into the flux bath. The flux bath ispreferably maintained at a temperature of to 212 F. The period ofimmersion of the ferrous article in the flux bath is preferably about 1to 2 minutes, with longer immersion times in this range being preferredwhen the lower recited temperatures are used. The flux produces auniform oxide resistant film or coating on the ferrous article whichprotects the clean surface of the ferrous article and provides a surfacewhich may be continuously uniformly wetted by molten aluminum. I

The preferred organic aromatic carboxylic acids of this invention aresalicylic acid and 5-chlorosalicylic acid. The preferred range ofconcentration of these acids is about 1 to 4 percent. With aconcentration under about 1 percent the maximum benefits of thisinvention are not obtained. When the concentrations of these acidsexceed 4 percent, the solubility of the acid is exceeded and excesschemical material tends to accumulate on the surface of the flux bath.This tends to impede the efficiency of the operation.

It has been found that these acids provide superior oxide protectionyielding excellent uniform coating. In addition, the resultant aluminumcoating has a desired, aesthetically pleasing smooth surface free fromoxide discoloration.

Subsequent to removal of the article from the flux bath, it is driedprior to application of the molten aluminum. This drying is preferablyeffected at a temperature of about 300 to 400 F.

The protected cleansed surface of the ferrous article is now in propercondition for application of the molten aluminum. This application ispreferably effected through hot dip aluminizing, i.e., immersion of theferrous article in a molten aluminum bath. it is preferred that themolten aluminum be at a temperature of about l,250 to l,400 F. and thatthe ferrous article be immersed in the molten aluminum bath for a periodof l to 2 minutes. This provides for adequate time to effect the desiredbonding of aluminum in the desired coating thickness, while avoidingexcess formation of the relatively brittle aluminum-ferrousintennetallic compound.

After withdrawal of the coated ferrous article from the molten aluminumbath, conventional means may be employed to remove any excess aluminumon the article.

In order to verify the effectiveness of the flux treatment of thisinvention, several tests were perfonned.

EXAMPLE 1 Several cast iron articles were first grit blasted to removescale and rust. They were then immersed in a pickling solution of 20percent concentration hydrochloric acid at 180 F. for l minute. Thespecimens were then removed and rinsed in hot water and immersed in a 3percent salicylic acid solution. After a 1 minute immersion period, thespecimens were air dried. The cast iron articles were then immersed in amolten aluminum bath at 1,400 for 1 minute. Upon withdrawal of thespecimens the excess aluminum was removed. A metallographic examinationof the articles revealed excellent bonding of the aluminum to the castiron and a smooth aesthetically pleasing surface appearance.

EXAMPLE 2 Example 1 was repeated with a group of mild steel articlesbeing divided into three groups. Three different flux baths having asalicylic acid concentration of 1 percent, 3 percent and 4 percent,respectively, were employed. One group of mild steel articles wasimmersed in each flux bath. After completion of the aluminizing process,a metallographic examination of the articles revealed excellent bondingand a smooth aesthetically pleasing surface appearance.

EXAMPLE 3 Example 1 was repeated with mild steel articles employing a0.125 percent S-chlorosalicylic acid flux. The specimens revealedexcellent bonding and the desired smooth coating.

EXAMPLE 4 A group of mild steel articles were treated in accordance withthe procedure outlined in example 1 except that the flux bath containedsalicylic acid in a concentration of 0.25 percent. The quality of theresultant aluminum coated articles was equal to that resulting from thetests of example I.

It will be appreciated that the process of the present affords a singleflux material which may be effectively employed with a broad range offerrous materials. Uniform oxide formation resistant protection andexcellent aluminum wetting and bonding properties are provided. Inaddition, the desired smooth aesthetically pleasing coating surfacecharacteristic is obtained.

In addition to the foregoing advantages, the process of this inventionproduces a desirable bright surface appearance and the resultant articleyields superior durability when the ferrous article is deformed aftercoating, as by bending.

Whereas particular embodiments of the invention have been describedabove for purposes of illustration, it will be evident to those skilledin the art that numerous variations of the details may be made withoutdeparting from the invention as defined in the appended claims.

We claim:

1. A process for coating a ferrous metal article with aluminum,comprising cleaning the surface of said ferrous article,

applying to the surface of said ferrous article a flux of about 0.125 to4 percent aqueous solution of an organic aromatic carboxyl acid havingone carboxyl group and a phenolic hydroxyl group,

drying said ferrous article, and

subsequently applying molten aluminum to said ferrous article.

2. The process of claim 1 including after cleaning said ferrous articlerinsing said article with water,

applying said flux through immersion of said ferrous article in a bathof said flux at a temperature of about to 212 F. for a period of about 1to 2 minutes, and

maintaining said flux bath at an acid concentration of about 1 to 4percent.

3. The process of claim 2 including said organic aromatic carboxyl acidis salicylic acid.

4. The process of claim 2 including said organic aromatic carboxylicacid is S-chlorosalicylic acid.

5. The process of claim 2 including subsequent to applying said flux butprior to applying said molten aluminum to said ferrous article dryingsaid ferrous article at about 300 to 400 F., and

applying said molten aluminum to said ferrous article by immersion ofsaid ferrous article in a molten aluminum bath for a period of about 1to 2 minutes at a temperature of about l,250 to 1,400 F.

6. The process of claim 5 including maintaining said flux bath at atemperature of about to 212 F. during the period of ferrous articleimmersion therein.

i i i

2. The process of claim 1 including after cleaning said ferrous articlerinsing said article with water, applying said flux through immersion ofsaid ferrous article in a bath of said flux at a temperature of about100* to 212* F. for a period of about 1 to 2 minutes, and maintainingsaid flux bath at an acid concentration of about 1 to 4 percent.
 3. Theprocess of claim 2 including said organic aromatic carboxyl acid issalicylic acid.
 4. The process of claim 2 including said organicaromatic carboxylic acid is 5-chlorosalicylic acid.
 5. The process ofclaim 2 including subsequent to applying said flux but prior to applyingsaid molten aluminum to said ferrous article drying said ferrous articleat about 300* to 400* F., and applying said molten aluminum to saidferrous article by immersion of said ferrous article in a moltenaluminum bath for a period of about 1 to 2 minutes at a temperature ofabout 1, 250* to 1,400* F.
 6. The process of claim 5 includingmaintaining said flux bath at a temperature of about 160* to 212* F.during the period of ferrous article immersion therein.